Adjustable electric filter system



Nov. 10, 1931. w. T. WINTRINGHAM ADJUSTABLE ELECTRIC FILTER SYSTEM Filed Jan. 19. 1928 2 Sheets-Sheet 1 A TTORNEY Nov. 10, 1931. w. T. WINTRINGHAM ADJUSTABLE ELECTIG FILTER SYSTEM 2 Sheets-Sheet 2 Filed Jan. 19. 1928 Patented Nov. 10, 1931 UNiTEn STATES@ PATENT ori-Fica f WILLIAM fr. WINTRINGHAM, o1*v BRooKI-:Ym NEW'YORK, ASSIGNORTOAMEMCAN'TELE: PHONE AND TELEGRAPH- COMPANY, A coIreonn'rronA on: NEW YORK ADJUSTABLE k:El,II'JEG'IIR'IC FILTER-r Application led. January 19, 1928. Serial No; 247,983...

tionalong the frequency scale before passing Still another object;

them vthrough the filter. ofmy invention is to provide for adjusting the cut-off frequency in a filter system by @adjusting the frequency ofA an alternating current generator. vAll these objects and` other; objects of my invention will become. apparent onconsideration of'a few examples. of the invention which I have chosen fordis- .closure in the following specification, taken with the appended claims andthe accom-v It will be understood;v

panying drawings. l that this specification relates principally to these examples of the invention and that the; il* scope ofthe invention willfhe indicatedV mf.

the claims.

Referring to the drawings, Figure 1 isa symbolic diagram of apparatus that may be,

employed in the practice of my invention;

used inexplanation of themodeof operationA ofthe apparatus of Fig. l; Figs. Sand 5 are symbolic diagrams showing modificationsa-s compared with Fig. l; and Figsland are coordinate diagramsto accompany Figs.'` 3` .2 at S7 and at R is areceiver to which certain .Y

and 5, respectively.

Referring to F 1g. 1, a source oflcomposite currents of various frequencies is `indicated i of the components, accordingtoefrequency,

between the source S andthe receiver R is capable-of adjustment .so that the frequency-V range deliveredtothe receiver shall hare Fig. 2 is a coordinate diagram that Willlloe suchiuppei' and lower limits` as may be fixed@ by the adjustment.

Fig. 2 is acoordinate diagram, the ordi:- nates representing; kilocycles and the ab scisseefrepresenting successive stagesftraced. 55. throughx the apparatus., in Fig. lf fromfleftstof. right. Numerals in F ig.4 2 notin parenthesesr represent frequencies. in-lrilocycles at the corresponding levels of., the diagram.. Nu-YM merals-in parentheses represent displacedfre-` ed 5 quencies.referredybaclr tothe original scale of frequencies Tin the source S. The constructionl and f mode of; operation of; thefapparatusroff. Fig.'` lA willnow be followed` through from; thesour'c'e Sto the receiver Rwithreference.- 65; to Figs. l and 2. The current components froml the vsourcev S range in frequency.` from 0.1m. -uptoffre--y quencies considerably more,A than; 6, kc.. 0f this. range,. frequencies4 from. 0 to.- 6 kc.. areI 70, passed by the low pass filter LFi. Thea modulator Mlis supplied with.a.basio. cur.-l rent of frequency` l1l kc, fromthe; generator Gi, and this current is..modulated by' the composite current of range. from() to4 6k@ 75a Accordingly, the modulator output.v come prises thef two. sidebands from; llfdowntto.l 5 koand fromy ll-.up to 1T( i kc. This output, goesrto` the high. pass` filter HFl Whose cut-.-

off 'frequency isat'l2 kc., and which accord 80;. I

ingly passesaband from l2 tol-7 kc. corresponding in order to,k the frequencies. from.

l t'o 6. kof. inthe original frequencyrange-finf. v the1sourceS. 1

rlhe modulator M2 isv supplied. from the 85,-" generatori. GrzY with a. basic current.; of. frer- Vquency 1.7. kc. whichis modulated,byftheoutfputfrom the high ,passiilter HFL.. A000111# ingly, the outputfrom themodulator Mml comprises/the two sidebands, one rangingljgogf from glrc., down'V to4 0v and the; other from-7, 29kc, up.to.34 kc.. The low,l passffilter LAE-2.; withcritical frequency at `6.,.kc. .cutsoffg the upper of. these two sidebandsand-p asscsethef part of; the` lower.A from; O to 5- lrc.which 95.

corresponds inl inverted, order, with-.6 .to.- 11 are. delivered. The intermediate apparatus..

kc. ofthe original frequencyV range-in7` `the-f source S.,

.The modulator Ms is suppliedwithfbasic;

ator G3, and this is modulated by the range from the low pass lter LF2 so that the output from the modulator M3 comprises the two ranges from 10 down to 5'kc. and from 10 up to 15 kc. These ranges are applied on the input side of the high pass filter HF 2 whose cut-off frequency is at 12 kc. Accordingly, the components passed by the high pass filter HF 2 range in frequency from 12 to 15 kc., corresponding lto the range from 4 to 1 kc. in the source S. i

Again, the modulator M2r is supplied with basic current of frequency 16 kc. from the generator G2, and thiscurrent is modulated by the range of 12 to 15 kc. in the output fromv the high pass filter HF2. Accordingly, the output from the modulator M4 comprises the two sidebands from 4 down to 1 kc. and from 2S up to 81 kc. The low pass filter LFS, with cut-off at 6 kc., suppresses the upper sideband but passes the lower sideband to the receiver R.

Comparing the current range to the receiver R with that going through the low `.pass filter LF1y from the source S, it will be seen that the initial range from to 6 kc. has been trimmed below and above; the range from O to 1 kc. trimmed from below, and the range from 4 to 6 kc. being trimmed e '.from above. The range Vdelivered to the receiver R is found at the same partof the frequency scale as the range from which it isjderived in the source S.

In the system as'disclosed in Fig. 1, there A.are Vlow pass filters LF1,LF2, and LF2, all

alike, each with cut off at 6 kc.; and there are two high pass filters HF 1 and HF 2, alike, and out oft' at 12 kc. The two generators G2 and G2 are adjustable as to frequency, and adjustable together as indicated by the symbols in Fig. 1, so that G2 will always be 6 kc. higher than G1. Similarly, the two generators G3 and G4 are adjustable as to frequency and are linked so that the frequency in G2 will always be 6 kc. higher than in G2.

'With the generators G1 and G2 adjusted, respectively, at 11 and 17 kc., the frequency rangef'passed bythe filter HF'1 is the part that corresponds to the range from 1 ko. to

.6 kc. in the source S. But if `these frequencies are adjusted, say, down to and 16, respectively, it will lower the frequencies of the currents relatively to the cut-0E point of 12 cycles in the high pass filter HF1 and from modulator M2 will be from a certain frebeen trimmed by a desired adjustable sub-' quencies of the generators G3 and Glare adjusted up or down, the band passed will be wider or narrower and that the palrt cut off will be the part corresponding. to the upper part yof the initial range from 0 to 6'V kc. in the source S. Whereas by adjustment of the frequencies of generators G1 and G2, the part corresponding to the lower edgeof the initial range was trimmed as desired, now by adjustment of the frequencies of the gen erators G3 and G4 the part corresponding to the upper end of the initial range from O to 6 kc. is trimmed as desired.

,The range from the high pass filter HF2 has nowbeen trimmed to the desired width and the function of the remaining generator G4 is simply to displace and invert the frequency range on the input side so asto give an output corresponding in its location on the frequency scale to the desired selected components in the current from the source S.

lt will he seen that the systemof Fig. 1

operates as a band pass filter withboth its` upper and lower cut-off frequencies inde. pendently adjustable so that the band of frequencies passed ultimately may be adjusted to any width and any location on the frequency scale within limits set by the designl of the apparatus.

For certain purposes it may not be deemed necessary to have as much flexibility of adjustment as here provided'. Figs. 3 and 4 relate to a modification inwhich it is desired to separate out for study a narrow sub-bandfor the quantity of noise in each narrow band of, say l'kc. width into which the range from 0 to k5 kc. may be divided. Here only two modulators M1 and M2 are required with their corresponding independently adjustable generators G1 and G2,v and only three filters, of

low pass variety, two cutting off alike at 5 kc.

and one at 13 kc.

From the source S in Fig. 3 currents from 0 to 5 kc. go through the low pass filter LF1 to the modulator lV 1 where they modulate a basic current of 14 kc., giving two sidebands in the output from 14 down to 9 kc. and from 14`up to 19 kc. Thelow pass filter LF2 passes only that part of the lower sideband from 18 down to 9 kc. corresponding to the part ofthe initial range from 1 to 5 kc. This passed range of output current from low pass filter LF2 is applied to modulator M2v to modulate a basic current` of 17 kc. from the resume generator G2, and accordingly, in the output l with the same advantage as if it were at its original level in the frequency scale, instead of being displaced up 3 kc. as is the case at the right of Fig. 4.

Again, in some cases the desired adjustment may be as to the level at which a subband is selected, keeping theband of unchanged width. A systemthat fulfills this requirement is shown in Fig. 5 where only two modulators are employed and their generators are adjustable together to hold like frequencies in both. There are also in this system two low pass filters, alike, and both cutting off at 5 kc., and a single band pass filter with fixed cut-off frequencies at 11 andy It will be seen that the range from 0 to 5 kc. is passed from the source S through the low pass filter LFl and applied to modulate the basic current of l5 lfc. in the modulator M1 whose output accordingly comprises an upper side-band and the lower sideband from 15 down to 10 kc. The part of this lower sideband passed through the band filter BF is adjustable by adjusting` the frequencies up or down for the generators G1 and G2. As shown in Fig. 6, the part that corresponds to 2 to 4 kc. in the source S is the part passed by the band filter BF. As will readily be apparent, the modulator M2 displaces and inverts this range so that it is restored to its normal original position on the frequency scale and delivered. through the low pass filter LF2 to the receiver R. If the location on the frequency scale were immaterial, as was stated to be the case for Figs. 3 and 4, the modulator M2 and the low pass filter LFP, would be unnecessary.

It will be seen that I have provided a system and a method of operation by which one may, in effect, select currents of al desired frequency range from components of wider range, with adjustment of this selection to any desired limiting frequencies within the limits of design of the apparatus employed.

I claim:

1. The method of filtering a composite current with effective adjustment of a cutofl'` frequency, which consists in shifting the said composite current to a new range by adjusting the frequency difference between the new range and the old one and kfiltering thereafter at a fixed cut-off frequency intermediate to said' new` range. v Y

v 2. vThe method which consists insshifting i a composite current to a new frequency range by a certain frequency difference, then? filteringfwitha fixedcut-off frequency. and adjusting the ,effective cut-off frequency relatively to the `initial'range `by adj'ustingthe said frequency; difference so as to` bring the newfrequency range to a relation with said fixed 'cut off frequency where the latter vwill be at the desired proper intermediate value. u 3. Infiltering a composite current with a vfixed filter cut off frequency, the method of A adjustmentof the cut-od frequency which comprises modulating the current with a current of single definite frequency and varying the said last mentioned frequency to 'bring a desired proper'interinediate frequency of the modulator output range to the value of the filter cut off Vfrequency and'thereby effect the adjustment desired. i

Y 4.. The method. of filtering a composite current' with adjustment of a cut-off frequency, j

which comprisesgenerating a current ofy a certainV definite frequency', modulating it b the initial composite current, filtering wit a" fixedA cut-od` frequency, frequency vof the said generated current whereby the modulated current is shifted in range relatively to the fixed filter cut-0E frequency so as to bring an intermediate frequency of the range ofthe said modulated current to the'desired proper Value ofl the said cut off frequency.

5. The method of adjusting the effective cut-off frequency of a filtered composite current of various frequencies, which consists in generating a carrier current, modulating it by said composite current, filteringV at a fixed cut-off frequency, and adjusting the' frequency of saidy carrier current yand thereby cutting off the modulated current at a frequency corresponding to the desired intermediate frequency inthe said composite current.

6. The method of filtering out a desired frequency band from a composite current with adjustment of a cut-off frequency, which consists in generating a carrier current, modulating it by the initial composite current, filtering with a fixed cut-off, adjusting the frequency of the carrier current to vary the range relatively to the filter cut-off frequency, generating another carrier current and modulating it by the filtered current and thereby getting currents of desired frequency at the location on the frequency scale corresponding to the desired components in the'initial composite current. v

7. In combination, a source of composite current, a receiver, a filter with fixed cut-off frequency between them, means to shift the frequency range of the composite current on the input side of said filter by an adjustable and vadjusting the frequency dierence, and means on the output side of said filter to shift the range for the currents passed bythe filter, whereby a partial frequency rangeof components from the sourcewill be delivered to the receiver at their proper place in the frequency scale."

8. An adjustable filter system between a source oficurrent of mixed frequency components and a receiver, comprising a modulater with its input connected to said source, a generator of carrier current adjustable as to frequency for said modulator so as to bring the modulator output range to have a desired proper intermediate frequency thereof at a certain value, and a filter with its cut? off at that value to receive the Vmodulator Y output and pass a part thereof to said receiver.

9. An adjustable filter system comprising a source of current of mixed frequency, a

modulator to receive current from said source, a generator of a definite frequency for said modulator, means to adjust the frequency of said generator so that an intermediate value of the frequency range ofthe modulator output shall have a certain value, ay filter with xed cut-o frequency at that value to which the modulator output is delivered, and a re ceiver connected on the output side of said lter. Y

10. An adjustable filter system comprising a source of current of mixed frequency, a modulator to receive current from said source, a generator of a definite frequency for said L modulator, means to adjustthe frequencyof said generator, a filter with fixed cut-off frequency to which the modulator output is delivered, another modulator to which the filter output is applied, a generator of definite frequency for said last-mentioned modulator, means to adjust this frequency, and another filter through which the output from the lastmentioned modulator output is passed to the said receiver. Y f

In testimony whereof, I have signed my name to this specication this 18th day of January, 1928. y

WILLIAM T. WINTRINGHAM. 

